The invention relates to a continuous rolling mill for the production of seamless tubes starting from hollow intermediate forgings fitted onto respective mandrels.
In particular the invention relates to a continuous rolling mill of the type with crossed stands, that is to say, comprising a plurality of rolling stands inclined alternately to the rolling axis and operating in a so-called retained-mandrel manner.
In continuous rolling mills of the said type, the rolling stands are supported by respective support structures firmly anchored to the ground and generally of excessive size to enable them to withstand safely and effectively the thrusts generated during the rolling process and oriented in directions parallel to the rolling axis.
Each stand of such a rolling mill essentially comprises a pair of working rolls with respective roll chocks, essentially clutch-type members for connecting the working rolls to respective driven shafts, as well as a plurality of mechanical, electrical, hydraulic and/or pneumatic connections and the like, for effecting a whole series of operations, other than rolling, but basically to achieve good operation of the rolling mill.
Among these operations, a particular one which is recognized to be important is the changing of the working rolls of one or more rolling stands simultaneously.
For this operation, until now, the entire stand, including the rolls to be changed, has been replaced by another stand provided with the new working rolls required. For this purpose each stand of a continuous rolling mill of the type under consideration has been designed and formed as a unit which can be manipulated individually and is structurally independent of the other stands so as to allow it to be removed from and inserted into the train of rolls independently of the rest of the stands.
Each stand is releasably fixed in a suitable seat formed in the support structure of the rolling mill by means of locking means and devices the sizes and weight of which can easily be imagined, given the considerable weight of a rolling mill stand of the type under consideration (on average about 20 to about 50 tonnes) and the considerable forces and thrusts in play during the rolling. It is well known that the support structure of a crossed-stand rolling mill, as well as constituting a massive part, also determines the values of the distances between the stands, values which the most up to date rolling technology would wish to reduce to a minimum, if not entirely eliminate.
The changing of the working rolls according to the known art involves a whole series of operations which are complex to carry out as well as requiring considerable and by now, unacceptable periods of time. Indeed the operations of releasing the stands under consideration from the support structure of the rolling mill and of lifting and transferring these stands away from the train of rolls, must always be preceded by a whole series of other operations relating to the disconnection of the hydraulic and/or pneumatic, electrical lines etc. and also the disengagement of the working rolls from their drive shafts. All these operations must then be repeated during the connection of a new stand in the train of rolls.
Thus, when in order to save time, it is required to change several stands simultaneously, there is a further considerable inconvenience, which is the need to use lifting and transfer machines and apparatus of considerable size and power which, in addition to the recognized operating difficulties, involve considerable power consumption, maintenance and deppreciation costs. To this end, account should also be taken of the fact that, in the optimum case, a crossed stand rolling mill of the type under consideration should be provided with two sets of stands of each caliber and, by way of compromise, with two sets of complete stands. The consequent disadvantages of costs and space necessary for such equipment have been recognized for a long time.
The object of the present invention is to provide a crossed-stand continuous rolling mill, particularly for the production of seamless tubes, by the so-called retained-mandrel technique, having structural characteristics whereby changing of the working rolls of one or more of its stands may be effected, while overcoming all the disadvantages mentioned with reference to the known art.